The following HTMLViewDefinition has a wrong layout when run:

HtmlViewDefinition view = new HtmlViewDefinition();
view.RowTemplate.Rows.Add(new RowDefinition());
view.RowTemplate.Rows.Add(new RowDefinition());
view.RowTemplate.Rows.Add(new RowDefinition());
view.RowTemplate.Rows[0].Cells.Add(new CellDefinition("column0", 0, 1, 1));
view.RowTemplate.Rows[0].Cells.Add(new CellDefinition("column1", 0, 1, 3));
view.RowTemplate.Rows[0].Cells.Add(new CellDefinition("column2", 0, 1, 1));
view.RowTemplate.Rows[1].Cells.Add(new CellDefinition("column3", 0, 1, 2));
view.RowTemplate.Rows[1].Cells.Add(new CellDefinition("column4", 0, 1, 1));
view.RowTemplate.Rows[2].Cells.Add(new CellDefinition("column5", 0, 1, 1));

The layout puts column5 over column1.

A possible workaround would be to refresh the rows in the grid's SizeChanged event handler:
        private void RadGridView1_SizeChanged(object sender, EventArgs e)
        {
            radGridView1.TableElement.ViewElement.UpdateRows(true);
        }